On Fri, Feb 21, 2020 at 09:22:46PM +0100, Peter Zijlstra wrote: > On Fri, Feb 21, 2020 at 11:05:36AM -0800, Andy Lutomirski wrote: > > > > - /* > > > - * Use ist_enter despite the fact that we don't use an IST stack. > > > - * We can be called from a kprobe in non-CONTEXT_KERNEL kernel > > > - * mode or even during context tracking state changes. > > > - * > > > - * This means that we can't schedule. That's okay. > > > - */ > > > - ist_enter(regs); > > > + nmi_enter(); > > > > I agree with the change, but some commentary might be nice. Maybe > > copy from here: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/idtentry&id=061eaa900b4f63601ab6381ab431fcef8dfd84be > > Fair enough; I'll add something to #DB and #BP for that. do_int3() is now like: @@ -529,19 +497,18 @@ dotraplinkage void do_general_protection } NOKPROBE_SYMBOL(do_general_protection); -dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) +dotraplinkage notrace void do_int3(struct pt_regs *regs, long error_code) { if (poke_int3_handler(regs)) return; /* - * Use ist_enter despite the fact that we don't use an IST stack. - * We can be called from a kprobe in non-CONTEXT_KERNEL kernel - * mode or even during context tracking state changes. - * - * This means that we can't schedule. That's okay. + * Unlike any other non-IST entry, we can be called from pretty much + * any location in the kernel through kprobes -- text_poke() will most + * likely be handled by poke_int3_handler() above. This means this + * handler is effectively NMI-like. */ - ist_enter(regs); + nmi_enter(); RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, @@ -563,7 +530,7 @@ dotraplinkage void notrace do_int3(struc cond_local_irq_disable(regs); exit: - ist_exit(regs); + nmi_exit(); } NOKPROBE_SYMBOL(do_int3); And I'm going to have to do another (few) patches for do_debug(), because that comment it has it patently false and I remember we had a bunch of crud for that. Let me dig those out.
